Hi Grunter. I used the 6.5x9 concentric coil just about all of last year. I would say I put close to 150 hours on it. Its a great coil for coins and jewelry. This year I used the 5x8DD because of some trashy areas I wanted to hunt. Its such a pain in the behind for me to change coils on the Atpro (big awkward hands and clumsy) I found several gold rings with the 6.5x9 and seven silver rings with it. If your just gonna hunt parks and sports fields etc for coins and jewelry,its a darn good coil. most of what I dug was between two and four inches with a few five and six inchers in there. I would like to leave the 5x8 on for trashy areas and I want to try some old home site hunts with it. It seems to go deeper than the 6.5x9. I would love to have 3 Atpros,one with the 6.5x9 for regular coin and jewelry,one with the 5x8 for trashy and woods hunts and one with the little sniper coil for totlots.shucks,might as well have a fourth with the stock 8.5x11 for more coverage and relics. Can you tell I hate changing coils on the Atpro? I have several other detectors but spend most of my hunts with the Atpro. If there are any specific questions you want to ask about the 6.5x9 I'll try and answer them.
I have not done any beach or surf hunting with the Atpro, so I can't say anything about that coil in that type of hunting.